Currently, Italian utility model no. 262995, filed with Italian patent application PN2005U000035, is known which claims a joint, for the detachable connection of two structural elements of a piece of furniture that mutually abut at right angles, comprising an accommodation body that can be associated with a first structural element and is adapted to engage a fixing element that can be associated with a second structural element and an actuation element that is arranged in the accommodation body and is adapted to cooperate with the fixing element so as to mutually fix the structural elements, the fixing element comprising a toothed head that is in one piece with a stem of a screw, the head being coupled rotatably within the accommodation body and the screw stem protruding from the accommodation body, the actuation element comprising a crown gear that is adapted to actuate the head in order to screw the screw stem into the second structural element.
This solution suffers drawbacks: a high production and assembly cost is in fact noted, due to the structural complexity of the joint, the need to provide the joint in various sizes/dimensions as a function of the thickness of the panel, the need to use the joint on panels with high minimum thicknesses, a considerable aesthetic impact since the joint exposes the flat edge that must be applied so as to affect one edge of the panel, and the need to provide two holes/seats on the panel for the placement of the accommodation body and of the pin, the execution of which is complicated.
The accommodation body has a cylindrical shape and is divided diametrically into two components, which must be joined in order to clamp the crown gear and the fixing element: a high degree of clamping might not allow optimum interaction between the gears, while clamping provided with the presence of plays might lead to difficulty in activating the gears due to possible mutual jamming of the teeth.
Furthermore, the crown gear and the fixing element are embedded in the accommodation body: in case of maintenance on the crown gear it is necessary to remove the entire accommodation body from the panel and therefore open, in practice breaking it, the accommodation body in order to access the internal components; in practice, in case of maintenance, it is thus necessary to replace the entire joint; moreover, the panel is also ruined in this case.
This solution makes it necessary to provide a further hole in the panel in order to be able to perform any adjustment of a leveling foot associated with the piece of furniture.
Finally, this structure is bulky and is therefore difficult to install if thin panels are used.
WO 2008/076089 is also known which discloses a solution for obtaining the connection of construction elements such as a panel; this solution comprises a threaded bush and a frame that can be arranged within a hole provided transversely to the panel; the following are placed inside the frame: a first screw, provided with a crown-shaped head; a bushing, which is externally threaded and is associated rotatably with a first complementary thread provided axially to the frame; a precompressed spring; a second screw, the head of which has a seat for accommodating such spring and the stem of the first screw; a third screw, which is arranged transversely to such first screw and the head of which interacts with the head of the first screw, according to a crown gear-pinion system.
The elements contained in the frame are fixed stably to the structure of the frame by way of a first threaded ring, which is associated rotatably with a second complementary thread provided axially to the frame, at an end thereof, keeping in position the second screw, and by a second ring, which is associated rotatably with a third complementary thread provided tangentially to the frame, at one end thereof, keeping the third screw in position.
Moreover a solution is provided in which a hole is provided in a panel to allow adjustment of the second screw.
This solution, also, suffers drawbacks: the third screw, once screwed to the frame, is fixed in its position and is no longer removable and therefore it is not possible to perform any maintenance in case of malfunctions or wear.
Furthermore, in this solution the head of the first screw works in contrast with an externally threaded bush that is associated rotatably with the first complementary thread provided axially to the frame; if the bush loosens, optimum interaction of the head of the first screw with the head of the second screw is no longer permitted, thus making adjustment unattainable.
A similar remark can be made in relation to the rotatable connection of the second screw to the frame by means of the bush.
This solution is structurally complicated, due to the large number of components that constitute the device, requiring a long and laborious preassembly of the various components to the frame, furthermore using a spring that is partially pre-compressed.
This solution, also, makes it necessary to provide an additional hole in the panel in order to be able to perform any adjustment of a leveling foot associated with the piece of furniture.
Finally, this structure, also, is bulky and difficult to install in thin panels.
U.S. Pat. No. 5,743,670A is also known which discloses a joining device, accommodated within a body or structural housing or frame, which is constituted by: a ring gear; a shell that accommodates the stem of the ring gear; a helical spring; a pinion gear; a coupler shaft; a front support.
The coupler shaft is a multi-segment constituted by: a cylindrical segment, which is accommodated at one end inside the shell; a cylindrical central segment, which is provided with a longitudinal retainer slot for a key; a cylindrical collar; a cylindrical coupling segment, which is accommodated in the front support and comprises a longitudinal shaft with a non-threaded segment and a threaded end.
The assembly method of the present known solution provides for a large number of constructive steps and furthermore such solution is structurally complicated due to the large number of components that constitute the device, requiring a preassembly of the various components to the frame that is long and laborious, furthermore using a spring that is partially pre-compressed and additional mechanical means or welds or adhesives as elements for fixing the shell and the front support to the body.
The large number of components, moreover, prevents the application of the device in particularly thin panels.
This solution is also particularly expensive in terms of production costs, due to the large number of components required, and in terms of cost and time required for preassembly of the components.
Finally, in this background art document it is found that maintenance or replacement of the activation element, i.e., of the pinion gear, is long, complicated and laborious, since it requires the complete disassembly of the joint as the pinion gear is the first element that is assembled during assembly and since it is not possible to extract it from the opening as the head of the pinion gear has a larger diameter than the opening.